The gain of an emitter-coupled differential amplifier connection of first and second transistors of a particular conductivity type can be controlled by supplying the collector current of the first transistor to a first controlled current splitter, by supplying the collector current of the second transistor to a second controlled current splitter identical to the first controlled current splitter, by controlling the first and second controlled current splitters using the same control signal, and by cross-coupling the current splitter output currents for application to the load, thereby to obtain constant quiescent load current despite change in gain responsive to change in the value of the control signal. Each controlled current-splitter comprises a respective pair of emitter-coupled further transistors receiving control voltage between their base electrodes, having the current to be split flowing through an interconnection between their emitter electrodes, and having the split portions of the current flowing through their respective collector electrodes. These third, fourth, fifth and sixth transistors are similar to each other in structure, are proximate to each other within an integrated-circuit, and are of similar conductivity type to the first and second transistors. The foregoing type of gain-controlled amplifier is disclosed in U.S. Pat. No. 4,471,311 issued Sep. 11, 1984 to Hirata and entitled "DETECTOR CIRCUIT HAVING AGC FUNCTION". The foregoing type of gain-controlled amplifier is also disclosed in U.S. Pat. No. 4,928,074 issued May 22, 1990 to Sato et alii and entitled "AUTOMATIC GAIN CONTROL CIRCUIT".
A problem with this gain-controlled amplifier is that as the control voltage between the base electrodes is reduced to zero, any swing past zero causes the controlled-gain amplifier to exhibit increasing gain with an attendant phasing reversal. This characteristic is extremely unattractive in certain applications. For example, in an automatic gain control (AGC) system, under certain conditions this signal-phase-reversal characteristic can undesirably cause the AGC to increase gain rather than decrease gain under strong signal conditions. The just described shortcoming of the previously known gain-controlled amplifier with constant quiescent load current with changes in gain was noticed by the inventor, who sought a controlled gain amplifier in which this shortcoming was overcome without losing the feature of constant quiescent load current with changes in gain and without losing any range in the output voltage swing for given operating supply voltage.